Eccentric grinding machine

ABSTRACT

The eccentric grinder includes a housing, a griding disk on which a grinding paper is held, an eccentric shaft on which the grinding disk is nonrotatably mounted and a mechanism for changing a grinding movement of the grinding disk having at least one fixed friction or toothed rim. At least one exchangable reversible intermediate plate (17,37) is provided for the grinder attachable to the eccentric shaft and each having at least one other friction or toothed rim (21,22). In operation, one of the intermediate plates (17,37) is placed between the housing (6) and the grinding disk (24), which, when engaging the fixed friction or toothed rim (34,35) with one of its friction or toothed rims (21,22), causes a rotary motion of the grinding disk (24) in addition to an eccentric motion.

BACKGROUND OF THE INVENTION

The invention is based on an eccentric grinder or grinding machine. Aneccentric grinder is known having an eccentric shaft and a grinding diskattached nonrotatably to the eccentric shaft as well as a device forchanging the grinding movement of its grinding disk with at least onefixed toothed rim, wherein an outer region of the grinding disk isarranged without connection to the rest of the parts of the grinder andis spaced axially from the latter and the grinding disk is attached tothe eccentric disk in a central portion. In such a grinder, as isdescribed in DE-OS No. 36 09 441, the toothed rims of the eccentric gearunit are fastened partly to a toothed ring and partly directly to thegrinding disk. As a result, a pressure exerted on the grinding disk edgeduring work leads to twisting of the toothed rim arranged on thegrinding disk due to the elasticity of the latter and accordingly leadsto meshing difficulties in the eccentric gear unit. Moreover, the gearunit comprising six toothed rims is relatively costly.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an eccentricgrinding machine, in which the above-mentioned difficulties areeliminated.

This object, and others which will be made more apparent hereinafter, isattained in an eccentric grinding machine comprising a housing, aneccentric shaft, a grinding disk and a device for changing a grindingmovement of the grinding disk having at least one fixed friction ortoothed rim in a fixed relationship with the housing, the grinding diskbeing nonrotatably fixed in a central portion thereof with the eccentricshaft and an outer region of the grinding disk being arranged withoutconnection to a remaining group of parts of the grinder and spacedaxially therefrom.

According to the invention at least one exchangeable, reversibleintermediate plate is provided for the grinder. Each of the intermediateplates is provided with at least one other friction or toothed rim. Inoperation one of the intermediate plates is mounted on the eccentricshaft and is engagable with the fixed friction or toothed rim having thefixed relationship with the housing to cause a rotary motion of thegrinding disk in addition to an eccentric motion.

In contrast, the eccentric grinder, according to the invention, has theadvantage that the grinding disk has no gear unit parts and is connectedonly in its central part with the next structural component part so asto be fixed with respect to rotation relative to it. This enables theuse of elastic plastic for the grinding disk, without deformations ofthe disk being propagated into the gear unit. Moreover, the cost of thegear unit is reduced because two of the toothed rims of the prior artcan be dispensed with.

It is particularly advantageous that the intermediate plates extend upto the eccentric shaft and accordingly have a heat conductingconnection. The heat occurring in the bearings of the eccentric shaftcan accordingly be conducted into the intermediate plate and can beconveyed from the latter to the air flow entering through theventilation openings. Moreover, the ventilation openings facilitate themanual removal of the intermediate plate.

The use of four differently constructed intermediate plates or twointermediate plates with two different sides, respectively is alsoadvantageous. This enables a total of four grinding movements of theeccentric grinder of different degrees of coarseness.

Since the toothed rims connected with the housing are constructed fromplastic and the toothed rims of the intermediate plate are constructedof wear-resistant metal, or vice versa, wear occurs on one side of theplastic toothing, which can be easily exchanged. When the grinding diskis provided with fourteen properly spaced ventilation openings,commercially available six-hole grinding papers as well as those witheight can be used holes.

BRIEF DESCRIPTION OF THE DRAWING

The objects, features and advantages of the present invention will nowbe illustrated in more detail by the following detailed description,reference being made to the accompanying drawing in which:

FIG. 1 is a partially cross-sectional, partially side elevational, viewof a grinder according to the invention;

FIG. 2 is a perspective view of a fan wheel and an intermediate platefor the grinder of FIG. 1;

FIG. 3 is a plan view of a grinding disk for the grinder of FIG. 1showing ventilation openings.

DETAILED DESCRIPTION OF THE INVENTION

An eccentric grinder 1 has a motor housing 2 and a grip stock 3 which isarranged above a gear unit housing 4 for an angular gear unit with powertake-off shaft 5. A fan housing 6 which is provided with an exhaustconnection piece 7 is fastened to the housing 4. A fan wheel 8 which issecurely connected with the power take-off shaft 5 is located in the fanhousing 6. An eccentric shaft 9 with eccentricity X relative to the axisof the drive shaft 5 is inserted in the fan wheel 8 from below andsupported by the bearings 10 and 11. The eccentric shaft 9 has a collar12 and a rectangular end portion 13 with an internal thread for afastening screw 14.

An intermediate plate 17 with a rectangular central opening 18 isattached to the end portion 13. The intermediate plate 17 preferablyconsists of aluminum which is provided with a hard, wear-resistantsurface by anodization. The intermediate plate 17 has a raised ring 19at both sides, which raised ring 19 rests against the collar 12 of theeccentric shaft 9 for the purpose of centering. The intermediate plate17 has ventilation openings 20 radially outside the ring 19. Theintermediate plate 17 carries, on each side at the outer edge, afriction or toothed rim 21, 22 preferably of different diameters. Thetoothed rims 21, 22 can be constructed of aluminum, the basic workmaterial of the intermediate plate 17, or plastic. A grinding disk 24contacts the intermediate plate 17 with its raised central area 23. Itis likewise attached to the end portion 13 with its central rectangularopening 25. The grinding disk 24 carries a collar 26 which projectsforward so as to face the intermediate plate 17. An elastic support 27is placed on the grinding disk 24. The grinding disk 24 and the support27 have ventilation openings 28, 29. The ventilation openings 20 and 28and 29 are arranged in such a way that they lie over one another so asto be aligned when the intermediate plate 17 and the grinding disk 24are placed on the rectangular end portion 13. A grinding paper 30 isfastened to the support 27, e.g. by a loop-and-hook locking arrangement.

A toothed plate 31 is fastened to the stationary fan housing 6 by threescrews 32. The toothed plate 31 has pins 33 which engage incorresponding recesses in the fan housing 5 for the purpose of securingagainst rotation and for centering. The toothed plate can also befastened to the fan housing 6 by snap connections instead of screws 32.The toothed plate 31 has two fixed friction or toothed rims 34, 35 ofdifferent diameters on the side facing the intermediate plate 17. Thesefixed friction or toothed rims 34, 35 can be made to be engagable withthe toothed rims 21, 22 on the intermediate plate 17 depending on whichside of the reversible intermediate plate 17 faces the fixed friction ortoothed rims 34, 35. The toothed rims 34, 35 are constructed either fromplastic or a wear-resistant metal, so that there is a metal-to-plasticpairing with the toothed rims 21, 22, in which wear can occur only atthe plastic toothing which is easily exchangeable. The amount of thedifference in the reference diameters of the toothed rims 22 and 34 andthe amount of the difference in the reference diameters of the toothedrims 21 and 35 corresponds to twice the eccentricity X. Friction rims,e.g. with a rubber layer, can also be used instead of toothed rims 21,22, 34, 35.

FIG. 2 shows a second intermediate plate 37 which has rims 38, 39 on thecircumference which correspond to the toothed rims 21, 22 on theintermediate plate 17, but which are toothless. In the central area, theintermediate plate 37 has a raised ring 40 at both sides and a centralrectangular opening 41 just like the intermediate plate 17. Theventilation openings 42 correspond to the openings 20. The intermediateplate 37 has connector pieces 43 on one of its two sides, whichconnector pieces 43 extend radially outward from the ring 40 and can beinserted into recesses 44 in the fan wheel 8 in a positive-lockingmanner. A connection is accordingly formed between the fan wheel 8 andthe intermediate plate 37 such that they are fixed with respect torotation relative to one another. There are no connector pieces 43 onthe rear side, not shown, so that the intermediate plate 37, when facingthe fan wheel 8 with the rear side, can rotate freely without contactingit, as is also the case with the intermediate plate 17 (see FIG. 1).

FIG. 3 shows the arrangement of the ventilation openings 28 in thegrinding disk 24. Six of the openings are arranged symmetrically withrespect to a circle on a diameter 46 of approximately 80 mm andapproximately eight openings 47 on a diameter of approximately 65 mm.

The basic operational principles of the drive of the eccentric grinderhas already been described in DE-OS No. 36 09 441. As in the latter, twogrinding movements of different degrees of coarseness are possible withthe intermediate plate 17. When the toothed rim 22 engages in thetoothed rim 34, a medium-coarse grinding movement results withrotational movement of the grinding disk in the opposite direction ofthe eccentric movement. When the toothed rim 21 engages in the toothedrim 35, a coarse grinding movement is produced in which the rotationalmovement of the grinding disk is in the same direction as the eccentricmovement.

Two different grinding movements can likewise be produced with theintermediate plate 37, a fine grinding movement, when the intermediateplate can rotate freely, and a very coarse grinding movement when theconnector pieces 43 engage with the recesses 44 of the fan wheel.

When pressure is exerted on the edge of the grinding disk 24 during thegrinding process, the latter bends inward toward the fan housing 6. Thisis made possible because of a gap of approximately 1-2 mm between theinside of the grinding disk 24 and the respective rim 21, 22, 38, 39facing the grinding disk. On the other hand, an excessive bending of thegrinding disk is prevented when the grinding disk abuts at the rim 21,22, 38, 39.

The fan wheel 8 fulfills a number of functions. In addition to producingthe eccentric movement and compensating for imbalances, it produces asuction air current which simultaneously serves to cool the bearings andthe gear unit. Air which is charged with grinding dust is sucked throughthe ventilation openings 29 and 28 in the grinding disk as well as 20 inthe intermediate plate and discharged again via the exhaust airconnection piece 7. The intermediate plate 17 and 37, respectively, atwhich the heat occurring in the bearings 10 and 11 is dissipated via theeccentric shaft 9, is simultaneously cooled by the air flow.

The intake of secondary air through the gap between the grinding disk 24and the fan housing 6 is extensively prevented by the labyrinth effectof the collar 26 of the grinding disk and the rim 21, 22, 38, 39 of theintermediate plate 17, 37, which rim 21, 22, 38, 39 faces the grindingdisk.

The invention is not limited to the shown embodiment example. Instead ofthe two reversible intermediate plates 17 and 37, four individual platescan also be used, each of which can be securely connected with a singlegrinding disk in the central area. This would also result in a flatterconstruction of the grinder.

However, the four grinding movements can also be produced by a singleintermediate plate which carries the two differently dimensioned toothedrims on the same side and whose connector pieces, which can be insertedin the fan wheel, can be detached, folded back or switched from theoutside during the fine, medium-coarse and coarse grinding movements. Inthis case, the toothed rims, which are connected with the housing so asto be fixed with respect to rotation relative to it, would be axiallydisplaceable, so that either one or the other or neither of them engageswith the toothed rims of the intermediate plate. This has the advantagethat the different grinding movements can be adjusted from the outsidewithout removing the grinding disk.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofstructures differing from the types described above.

While the invention has been illustrated and described as an eccentricgrinding machine or grinder, it is not intended to be limited to thedetails shown, since various modifications and structural changes may bemade without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed is new and desired to be protected by Letters Patent isset forth in the appended claims.

We claim:
 1. In an eccentric grinder comprising a housing, an eccentricshaft, a grinding disk and a device for changing a grinding movement ofthe grinding disk having at least one fixed friction or toothed rim, thegrinding disk being nonrotatably fixed in a central portion thereof withthe eccentric shaft and an outer region of the grinding disk beingarranged without connection to a remaining group of parts of the grinderand spaced axially therefrom, the improvement comprising a plurality ofexchangeable, reversible intermediate plates (17,37), one of saidintermediate plates (17) being arranged between the housing (6) and thegrinding disk (24) in operation of said grinder, each of saidintermediate plates (17) being provided with a pair of friction ortoothed rims (21,22), which, when engaging said fixed friction ortoothed rim (34,35), causes a rotary motion of the grinding disk (24) inaddition to an eccentric motion.
 2. The improvement as defined in claim1, wherein two different ones of said fixed friction or toothed rim(34,35) are provided on the housing and two different ones of saidfriction or toothed rims (21,22) are provided on the intermediate disk,one of said friction or toothed rims on the intermediate disk beingdirected radially outwardly and the other of said friction or toothedrims on the intermediate disk being directed radially inwardly, saiddifferent friction or toothed rims (21,22) on the intermediate diskcooperating with said fixed friction or toothed rim (34,35) on thehousing so as to produce a rotational motion of a different rotationalspeed depending on which of said friction or toothed rims (21,22)cooperates with said fixed friction or toothed rims (34,35).
 3. Theimprovement as defined in claim 1, wherein said eccentric shaft (9) hasa noncircular cross-sectioned end portion (13), on which both theintermediate plate (17,37) and the grinding disk (24) are releasablymountable.
 4. The improvement as defined in claim 3, wherein theintermediate plate (17,37) has a central opening (25,41) having anoncircular cross section shaped equivalent to that of the noncircularcross-sectioned end portion (13) of the eccentric shaft (9), and thegrinding disk (24) is supported in a central region (23) around a ring(19,40) of the intermediate plate (17,37).
 5. The improvement as definedin claim 1, further comprising a fan wheel mounted on the eccentricshaft and wherein the grinding disk (24) is provided with a plurality ofventilation openings (28) and the intermediate plate (17,37) contactsthe eccentric shaft (9) and has a plurality of other ventilationopenings (20,42) through which air can flow from the ventilationopenings (28) of the grinding disk (24) to the fan wheel.
 6. Theimprovement as defined in claim 5, wherein the fan wheel is providedwith a plurality of recesses (44) and the intermediate plate (37) has atoothless rim, a ring (40) and four connecting pieces (43) extendingradially outwardly from the ring (40) engagable in a positive-lockingmanner in the recesses (44) of the fan wheel.
 7. The improvement asdefined in claim 6, wherein the intermediate plates are made of metaland the toothed rims (34,35) securely connected with the housing (6) areeasily exchangable and made of plastic.
 8. The improvement as defined inclaim 7, wherein said metal is die-cast aluminum.
 9. The improvement asdefined in claim 1, wherein the intermediate plate (17) is made of metalbut the toothed rims on said intermediate plate (17) are made of plasticand the toothed rims (34,35) connected with the housing (6) are made ofmetal.
 10. The improvement as defined in claim 1, wherein the grindingdisk is provided with fourteen ventilation openings (28), six of saidventilation openings being arranged symmetrically with respect to acircle of a diameter of approximately 80 mm and eight of saidventilation openings being arranged symmetrically with respect toanother circle of a diameter of approximately 65 mm.
 11. In an eccentricgrinder comprising a housing, an eccentric shaft, a grinding disk and adevice for changing a grinding movement of the grinding disk having atleast one fixed friction or toothed rim in a fixed relationship with thehousing, the grinding disk being nonrotatably fixed in a central portionthereof with the eccentric shaft and an outer region of the grindingdisk being arranged without connection to a remaining group of parts ofthe grinder and spaced axially therefrom, the improvement comprising anexchangable, reversible intermediate plate (17,37) arranged between thehousing (6) and the grinding disk (24), said intermediate plate (17)being provided with a pair of friction or toothed rims (21,22), which,when engaging said fixed friction or toothed rim (34,35), causes arotary motion of the grinding disk (24) in addition to an eccentricmotion.
 12. The improvement as defined in claim 11, wherein twodifferent ones of said fixed friction or toothed rim (34,35) areprovided in a fixed relationship to the housing and two different onesof said friction or toothed rims (21,22) are provided on theintermediate disk, one of said friction or toothed rims on theintermediate plate being directed radially outwardly and the other ofsaid friction or toothed rims on the intermediate plate being directedradially inwardly, said different friction or toothed rims (21,22)cooperating with said fixed friction or toothed rim (34,35) so as toproduce a rotational motion of a different rotational speed depending onwhich of said friction or toothed rims (21,22) cooperates with saidfixed friction or toothed rim (34,35).
 13. The improvement as defined inclaim 11, wherein said eccentric shaft (9) has a noncircularcross-sectioned end portion (13), on which both the intermediate plate(17,37) and the grinding disk (24) are releasably mountable.
 14. Theimprovement as defined in claim 13, wherein the intermediate plate(17,37) has a central opening (25,41) having a noncircular cross sectionshaped equivalent to that of the noncircular cross-sectioned end portion(13) of the eccentric shaft (9), and the grinding disk (24) is supportedin a central region (23) around a ring (19,40) of the intermediate plate(17,37).
 15. The improvement as defined in claim 11, further comprisinga fan wheel mounted on the eccentric shaft and wherein the grinding disk(24) has a plurality of ventilation openings (28) and the intermediateplate (17,37) contacts the eccentric shaft (9) and has a plurality ofother ventilation openings (20,42) through which air can flow from theventilation openings (28) of the grinding disk (24) to the fan wheel.16. The improvement as defined in claim 15, wherein the fan wheel isprovided with a plurality of recesses (44) and the intermediate plate(37) has a toothless rim, a ring (40) and four connecting pieces (43)extending radially outwardly from the ring (40) which engage in apositive-locking manner in the recesses (44).
 17. The improvement asdefined in claim 14, wherein the intermediate plate is made of metal andthe toothed rims (34,35) securely connected with the housing (6) areeasily exchangable and made of plastic.